1. Field of the Invention
This invention relates to a spider for a drum brake and, more specifically, to such a drum brake which is found in heavy duty truck and trailer axle configurations and includes dual web brake shoes and an actuation means which is supported at a location axially separated from the location for the support of the pivotal ends of the brake shoes.
2. Description of the Prior Act.
It is not uncommon in the heavy duty truck and trailer field to utilize drum brakes which employ a rotary cam actuation means. Typically such brakes include a pair of brake shoes having adjacent ends pivotally mounted on a pair of pivot pins supported by a brake spider which is secured to the axle spindle. A rotatable actuating cam is mounted at the opposite end of the spider and disposed between the other ends of the brake shoes. Rotary movement of the cam causes each of the brake shoes to move outwardly about the pivot pins to contact the inwardly facing friction surface of the brake drum.
For such heavy duty brake installations, the brake shoes are relatively wide and are commonly of the dual web type. Typically, each dual web brake shoe is supported at its pivital end by structure which is centrally located on the brake shoe and the ends of each pivot pin extend outwardly from opposite sides of the support to be recieved within web bores or recesses in each of the webs. The webs at the other end of each brake shoe support a roller means therebetween which makes rolling contact with the actuating cam and receives the actuation force therefrom. However, the actuating cam cannot be supported at a location between the brake shoe webs, as can the pivot pins, because the rotatable cam is physically positioned in this region. Therefore, the support for the rotary cam actuation means is typically axially separated from a location between the webs and central of the brake shoes. As a result, brake spiders utilized in brakes of this type include support structure which is aligned between the webs of shoes at one end and which is offset to support the rotary cam actuation means at the other end.
U.S. Pat. Nos. 2,167,607; 2,957,706; 3,131,583 and 4,157,747 disclose brake spider configurations of this type and are usually forged to provide a thickened, reinforced structure having sufficient strength to withstand the axially separated forces acting on the spider during braking operation. While brake spiders of this type have been satisfactorily employed for a number of years, it is always desirable to reduce the overall weight of such heavy duty brake installations and to reduce the cost of their manufacture and assembly.